Abstract: In the field of controlled nuclear fusion, the tokamak (a toroidal vacuum chamber which uses magnets to confine and heat plasma to fusion temperatures/ pressures) is one of the most promising candidates for a fusion reactor. The spherical tokamak (ST) has been a good candidate for tokamak reactor designs since its inception in the 1980s. The design boasts economic benefits that are especially important for labs looking to build tokamaks for research as the ST cuts down on the cost of the large magnets needed to establish the strong magnetic fields in a tokamak. One of the problems with the ST design is less space for a centre solenoid which can be used to induce plasma current. Using the iron-core tokamak STOR-M we are able to study plasma performance as the core becomes increasingly magnetized. This effect is of some concern to the tokamak community as it becomes more pronounced as the size of the tokamak core region (the hole in the tokamak torus) decreases.

Who (supervisor): Sayf Gamudi Elgriw (Chijin Xiao)Venue: College of Engineering Research Day, Sept. 20, 2012.Abstract: The active control of magnetohydrodynamic (MHD) instabilities has been an intriguing topic in tokamak fusion research. Several methods have been developed to control the onset of MHD instabilities in tokamak plasmas. One of the methods involves the use of radial magnetic perturbations generated by helical coils wound around a tokamak. The purpose of influencing the plasma with resonant magnetic perturbations (RMP) is to manipulate the radial topology of magnetic islands through resonant interaction. A series of experiments has been carried out in STOR-M to examine the effect of the RMP on the (2, 1) tearing modes during an active MHD and low q ohmic discharge. The amplitude and frequency of (2, 1) island fluctuations were significantly reduced after the activation of RMP. Moreover, a phase of improved plasma confinement, characterized by a reduction in Hα emission level, a reduction of hard X-ray (HXR) emissions, and an increase in soft x-ray (SXR) emission, has been induced after the application of RMP. It has also been observed via ion Doppler spectroscopy (IDS) that RMP can strongly affect the plasma rotation in STOR-M. It has been found that during the RMP pulse, the toroidal velocity of CIII impurity (located at the plasma edge) increases in the co-current direction. However, the toroidal velocities of OV and CVI species (located near the plasma core) change direction from counter-current to co-current. Other effects of RMP, i.e. the reduction of floating potential and the increase of density, have been observed at the plasma edge using rake probes.

Plasma Ion Implantation is a materials processing technique that can be used to modify the surface and subsurface structure of a material. A voltage bias applied to a conductive target immersed in plasma introduces a buried layer of impurities in the existing material. This processing technique has been applied to the modification of Si to produce silicon-based light emitting diodes (LEDs) with some success. Bulk silicon is not a light emitter due to its indirect band gap, but any photonic integration for multicore processing needs to be silicon based in order to be scalable for mass production. The work presented here is based on introducing carbon to a silicon wafer to introduce a buried layer of SiC – a known blue light emitter. With the introduction of a buried layer with significantly different stoichiometry from the native material, we see the appearance of delaminated blister features in the layer.